1. Technical Field
The present invention relates generally to an illuminant device such as a headlamp which may be employed in automotive vehicles, and more particularly to an illuminant device designed to improve the dissipation of heat, as generated by circuit components during operation.
2. Background Art
A plurality of lighting modes are known between which an operation of lamps used as illuminants for given areas is switched as needed. For instance, headlamps installed in automotive vehicles are usually switched between a low beam mode in which a beam of light is emitted to a short range area and a high beam mode in which a beam of light is emitted to a long range area. Lighting systems such as night vision or night view (trade mark) systems are also known which operate in an IR (infrared) mode to emit infrared light in order to increase a vehicle driver's perception and seeing distance in darkness or poor weather. Further, lighting systems are known which are used in mobile objects such as automotive vehicles and operate in a DRL (Daytime Running Lamps) mode to turn on an illuminant in a daytime or in a position mode to turn on the illuminant in order to improve an operator's perception of the width of the mobile object.
Most mobile objects such as automotive vehicles are usually subject to limitations on locations or spaces where lamps or lighting control devices are to be installed. It is, thus, necessary to decrease the size of the lamps or the lighting control devices. The downsizing of the lighting devices is achieved by fabricating a plurality of lighting circuits for the respective lighting modes on a single circuit board.
The integration of the lighting circuits on the single circuit board will result in an increased density at which the lighting circuits are located, which leads to a decreased area of the circuit board required to dissipate heat produced by the lighting circuits. This causes the heat to be accumulated in the circuit board, thus resulting in an elevation in temperature of parts of the lighting control device and a failure in lighting the lamp. In order to alleviate such a problem, Japanese Patent First Publication No. 2000-195331 teaches installation of a heat radiator such as a heat sink on the circuit board to release the heat outside the circuit board.
The installation of the heat radiator, however, will consume an area of the circuit board, thus obstructing the downsizing of the lighting control devices and also result in increases in weight and production cost of the lighting control devices.
Additionally, production of the lighting control devices which are different in combination of the lighting modes from each other requires preparation of a plurality of circuit boards on each of which lighting circuits for one of the different combinations of the lighting modes are fabricated, which will also result in increases in type and manufacturing cost of the circuit boards.